The present invention relates to a power transmission device.
Conventionally, there has been known a power transmission device provided with a tubular first rotator having a bottomed tubular shape, a shaft-shaped second rotator arranged rotatably within the first rotator, and a clutch mechanism arranged between the first rotator and the second rotator. The first rotator is rotated by a drive force of a vehicle. The second rotator is arranged coaxially with the first rotator. The clutch mechanism couples the first rotator and the second rotator so as to transmit torque. As one kind of the power transmission device mentioned above, Japanese Laid-Open Patent Publication No. 2004-332758 discloses a power transmission device in which an input shaft portion projects from an outer surface of a bottom portion of the first rotator. Further, Japanese Patent No. 3256737 discloses a power transmission device in which a flange portion is provided in a propeller shaft, and a bottom portion of a first rotator is fastened to the flange portion by bolts.
The power transmission device described in Japanese Laid-Open Patent Publication No. 2004-332758 has a problem that it is impossible to employ a simple machining method, for example, the flow forming, and the machining cost of the first rotator is high. Further, in a power transmission device provided with an electromagnetic coil and controlling an engaging force of a clutch on the basis of an applied current to the electromagnetic coil, there is a case that the first rotator is formed of an aluminum alloy, as described in Japanese Patent No. 3256737. However, in the power transmission device mentioned above, it is impossible to transmit a sufficient drive force via an input shaft portion having a comparatively small diameter in the light of the strength, and there is a case where it is impossible to employ a structure in which the input shaft portion projects from the outer surface of the bottom portion of the first rotator.
Further, in the power transmission device in which the bottom portion of the first rotator is fastened to the flange portion by the bolts as described in Japanese Patent No. 3256737, since the bolts are screwed to the bottom portion of the first rotator from the flange portion, a space (or the thickness of the bottom portion) for forming bolt holes is necessary in the bottom portion of the first rotator. Further, since a plurality of through holes are formed in the flange portion, it is necessary to form the flange portion thick so as to avoid accompanying reduction of strength. This structure is disadvantageous in the light of weight savings and downsizing, particularly in reduction of axial length, and there is a room for improvement with respect to these points.